1. Field of the Invention
The present invention relates to a calender with a plurality of rolls having axes located in a press plane. The plurality of rolls are arranged such that adjacent rolls form a nip between each other, and the calender includes a control device to open and close the nips.
2. Discussion of Background Information
During the glazing of a paper web, the paper web is guided through a calender and, within the nips (or roll openings) of the calender, is pressed under pressure, and, if necessary, with an increased temperature. This method of pressure treatment in the calender determines the surface characteristics of the processed web. Thus, it is apparent that the quality of the web surface can be improved by increasing the number of the nips.
However, in many cases a high surface quality is not necessary or desired. In other words, a lower number of nips may be utilized to produce a web with adequate surface characteristics.
For example, it is known from EP 0 661 405 A1 to provide a calender with four rolls and three nips, and that the rolls are adjustable so that the calender includes three, two, or even only one nip. When less than three nips are utilized, the bottom nip or nips are closed, while the other, i.e., upper, nips remain open. The line load that effects the paper web can be altered in this arrangement, e.g., utilizing three deflection adjustment rolls. Moreover, the sequence of the nips is fixed, i.e., when both nips are closed, treatment in the third nip must follow treatment in the second nip. In this manner, possibilities of variation are somewhat limited.
Another calender is discussed in German Patent Application No. 196 31 056, in which a roll stack having several nips in a calender is combined with a roll pair having only one nip. Both roll stacks have a common roll and can be driven alternatively. However, in this case, the industrial expenditure is relatively high due to an additional deflection adjustment roll with two operational directions.